Gain control circuit



Dec. 6, 1938.

GAINCONTROL CIRCUI Filed May 2a, 1937 J. P. KINZER ET AL 2 Sheets-Sheet 1 A TENUAT/ON IVQTWORA GEAR/MG 6A1. VI'NOMETER MECHANISM BJ/ W JQP/(INZER INVENTORS ATTORN'V Dec. 6,1938; KINZER HAL 2,139,236

' GAIN CONTROL CIRCUIT Filed May 28, 1937 2 Sheets-Sheet WORK FIG. 5

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ATTORNEY Patented Dec. 6, 1938 GAIN CONTROL CIRCUIT John P. Kinzer, Hackensack, N. J., and Ira G.

Wilson, Brooklyn, N. Y., assignors to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application May 28, 1937, Serial No. 145,202

10 Claims.

This invention relates to gain control circuits and particularly to gain control circuits for maintaining constant attenuation on a transmission line.

pensation is made in the gain control circuits for the non-linear attenuation variations of the transmission line with temperature changes. A gain control circuit of the type under consider- One object of the invention is to provide a sigation is shown in the patent to F. A. Brooks, No. 5.: nal transmission line with a gain control circuit April 1937- having a linear operation with temperature In accordance with the invention, provision is changes that shall control the transmission line made to insure that the corrections made to the attenuation while compensating for the nontransmission line attenuation vary according to linear attenuation variations of the transmission the non-linear attenuation variations of the 10 line with temperature changes. transmission line with temperature changes. In Another object of the invention is to provide one form of the invention, a variable resistance a signal transmission line with a pilot-line gain in one arm of the bridge circuit is controlled accontrol circuit having a linear operation with cording to the Operation of h a v t temperature changes and including a bridge cir- Control mechanism to compensate for the noncuit operating galvanometer mechanism to conlinear variations of the transmission line attenutrol the transmission line attenuation that shall ation with temperature changes. compensate for the non-linear attenuation vari- The term pilot line as used in the specificaations of the transmission line with temperature t on is i e ded to c v not y a pilot line changes. comprising a separate pair of wires but also to A further object of the invention is to provide cover a pilot line comprising a direct-current a signal transmission line with a pilot-line gain path on the pair of wires comprising the transcontrol circuit having a linear operation with mission line. temperature changes and including a bridge cir- In the accompany drawings, 1 iS a cuit operating galvanometer mechanism to congremmatio w o a pilot-line gain control trol the transmission line attenuation that shall circuit constructed in accordance with the invary the bridge circuit operation to compensate vention. for the non-linear attenuation variations of the Fig. 2 is a dia m a i V ew o a odificat o transmission line with temperature changes. of the n C t c t S wn in 1 of he The attenuation of a signal transmission line drawings. is in many cases controlled and maintained sub- F 3 is a a ic V w Of a dificat o stantially constant by means of the so-called of the circuit shown in Fig. 1 wherein the repilot-line gain control circuit. A pilot lin is assistance of the pilot line is varied to compensate sociated with the signal transmission line so for the non-linear attenuation variations of the as to be subjected to the same temperature varytransmission line with temperature changes. ing conditions as the transmission line and forms Fig- 4 is a S of v s S w e onea one arm of a bridge circuit. The bridge circuit attenuation variations of the transmission line operates a galvanometer which in turn operates w th temp changesa galvanometer control mechanism either to con- F g. 5 s a diagrammatic e of co de er trol the gain of an amplifier in the transmission that may be employed in the feedback circuit line or to control pads in the transmission line. of the line amplifi r t0 compensate fo he non- The variation of attenuation in a transmission linear attenuation variations of the transmission line with temperature changes has been found ine w t e p e changesto be non-linear. The resistance variation of the F 6 is a diagrammatic V of he V r able pilot line with temperature changes is linear. resistance employed in the circuit of Fig, 2 to The resistance variation of the pilot line governs compensate for the non-linear attenuation varithe bridge circuit which, by means of the galations of the transmission line with temperature vanometer and the galvanometer mechanism, changes. govern the attenuation of the transmission line. Referring to Fig. 1 of the drawings, a trans- Thus the galvanometer and the galvanometer mission line comprising conductors I and 2, control mechanism have linear operation with which may be a pair of wires in a cable, has the temperature changes and effect linear changes in attenuation variations thereof corrected by the attenuation of the transmission line. Acmeans of gain control circuits 3. The gain concordingly a small error will be included in the trol circuits 3 control the attenuation variations operation of the gain control circuit unless comof the transmission line by governing the operation of a line amplifier 4. A transformer 5 is connected to the input circuit of the amplifier 4 and a transformer 6 is connected to the output circuit of the amplifier 4. The amplifier 4 is provided with a feedback circuit I joining the output and input circuits of the amplifier. The feedback circuit comprises an attenuation network 8, a manually adjustable condenser 9 and a condenser I D which is controlled by the gain control circuits 3.

The gain control circuits 3 comprise a pilot line I II which forms one arm of a bridge circuit I2. The pilot line I I is shown as comprising a separate pair of wires. However, it is to be understood that if so desired, the pilot line II may be a directcurrent path on the transmission conductors I and 2. The bridge circuit I2 comprises in addition to the pilot line arm a resistance arm I3, a variable resistance comprising sections I4 to I9, inclusive, and a variable resistance 20. The variable resistance is operated to rebalance the bridge after each operation of the gain control circuits. The resistance sections I4 to I9, inclusive, are controlled to compensate for the nonlinear attenuation variations of the transmission line with temperature changes. A battery 2| is connected between two opposite vertices of the bridge I2 and a galvanometer control mechanism 22 is connected across the other two vertices of the bridge I2. The galvanometer control mechanism may be of the type disclosed in detail in the patent to'J. A. Coy et a1. 2,017,654, October 15, 1935, or in the patent to Ulrich 1,647,383, dated November 1, 1927. The mechanism 22 operates a shaft 23 in accordance with the operation of the bridge circuit I2. The shaft 23 carries two beveled gear wheels 24 and 25 and the rotor winding 26 of a master motor 21. The master motor 21 is provided with a stator winding 28 directly connected to a source of alternating current 29.

The beveled gear wheel 25 meshes with a beveled gear wheel 30 which is connected through a set of gearing 3| to a shaft 32 carrying cam members 33 to 31, inclusive. The cam members 33 to 31, inclusive, control the operation of switch members 38 to selectively operate relays 39. The relays 39 respectively complete circuits for short-circuiting the resistance sections I4 to I9, inclusive. If the shaft32is continuouslyoperated in acounterclockwise direction, as viewed in Fig. 1 of the drawings, the relays 39 will be successively operated to successively short-circuit the resistance elements I4 to I9, inclusive. The beveled gear wheel 24 meshes with a beveled gear wheel 40 which in turn is connected through gearing H to a shaft 42. The shaft 42 carries a rheostat arm 43 which engages the resistance 29. The resistance 20 is varied to rebalance thebridge I2 for each operation of the galvanometer control mechanism 22.

The three-phase rotor winding 26 of the master motor 21 is connected to the rotor winding 44 of a service motor 45. The service motor 45 is provided with a stator winding 46 which is connected to the source of alternating current 29. The rotor winding 26 of the master motor 21 will be connected similarly to any number of other service motors which it may be desired to operate. The stator windings of any other service motors which may be connected to the master motor will be connected to the source of alternating current 29. The service motor '45, when connected as above described, will follow any movement of the master motor rotor 26. The rotor 44 of the service motor 45 controls the adjustable condenser III in the feedback circuit 1 by means of a shaft 4'! and pilot line.

gearing 48. A detailed description of the operation of the condenser II) in controlling the gain of the amplifier 4 is given in the above-mentioned patent to F. A. Brooks, 2,075,975, and, accordingly, a detailed description here is deemed unnecessary.

In case the transmission line comprising conductors I and 2 is subjected to a change in temperature, the pilot line II will be subjected to a like change which Will vary the resistance of the The bridge circuit I2 will have its electrical properties varied in accordance with the variation in resistance of the pilot line II. The bridge circuit I2 in turn effects operation of the galvanometer control mechanism 22. The galvanometer control mechanism 22 would have a linear operation with temperature changes unless compensating means were provided by the resistance sections I4 to I9, inclusive, by reason of the fact that the resistance of the pilot line I I has a linear variation with temperature changes. The galvanometer control means 22, by means of the shaft 23, beveled gear wheels 25 and 30, and the cam members 33 to 31, inclusive, controls the relays 39 to vary the resistance sections I4 to I9, inclusive, included in one arm of the bridge I2. The resistance sections I4 to I9, inclusive, are of such size as to compensate for the non-linear attenuation variations of the transmission line with temperature changes. The galvanometer control mechanism 22 also adjusts the resistance 20 to effect a rebalancing operation of the bridge I2. The master motor 21 is operated to control the service motor 45 and adjusts the feedback for the amplifier 4 so as to maintain the line attenuation substantially constant.

Referring to Fig. 4 of the drawings, curves are shown to illustrate the non-linear attenuation variations of the transmission line with temperature changes. The curve A in full lines indicates the gain or loss in decibels on the transmission line with changes in temperature. The curve is drawn with temperature variations as abscissas and decibel loss or gain as ordinates. The curve B indicates the normal gain of the amplifier 4 if no' compensation were provided for the nonlinear attenuation characteristics of the transmission line. The curve C indicates the amplifier gain characteristics where compensation has been eifected for the non-linear attenuation characteristics of the transmission line.

In Fig. 2 of the drawings is shown a modification of the circuit shown in Fig. 1 and like parts in Fig. 2, to those shown in Fig. 1, will be indicated by similar reference characters. The bridge circuit I2 in the circuit shown in Fig. 2 has a variable resistance 50 included in one arm thereof in place of the resistance sections I4 to I 9, inclusive, shown in Fig. 1 of the drawings. The shaft 23, which is operated by the galvanometer control mechanism 22, carries a beveled gear wheel 5I which is connected through a bevel gear wheel 49 and gearing 52 to a shaft 53 carrying an arm 54 for adjusting the resistance 50. The resistance 50 in the bridge circuit I2 of Fig. 2 of the drawings is shown in detail in Fig. 6 of the drawings. The shape of the resistance 55 is varied in a manner to compensate for the non-linear attenuation variations of the transmission line when the resistance arm 54 is operated linearly in accordance with temperature variations. The circuit shown in Fig. 2 of the drawings operates in the same manner as the circuit shown in Fig. 1 of the drawings with the exception of the control of the resistance which compensates for the non-linear attenuation variations. of the transmission line.

In Fig. 3of the drawings is shown a modification of the invention wherein compensation for non-linear attenuation variation of the transmission line with temperature changes is effected by controlling a resistance 55 in the circuit of the pilot line II. The resistance 55 is controlled by the galvanometer control mechanism 22 in the same manner as the resistance 50 in the circuit shown in Fig. 2 is controlled by the galvanometer control mechanism. A beveled gear wheel 56 onthe shaft 23 meshes with a beveled gear wheel 51. The beveled gear wheel 5'! is connected through gearing 58 to the shaft 59. The shaft 59 carries a resistance arm 60 which adjusts the amount of the resistance 55 included. in the pilot line H.

Like parts in the circuit shown in Fig. 3 to those shown in Figs. 1 and 2 have been indicated by similar reference characters. The operation of the circuit with the exception of the control of the resistance of the pilot line is similar to the operation of the circuits shown in Figs. 1 and 2 of the drawings.

It is also possible to compensate for the nonlinear attenuation variations of a transnnssion line with temperature changes by varying the shape of the condenser plates in the condenser H]. In Fig. 5 of the drawings, a condenser having the plates thereof varied to compensate for the non-linear attenuation variations is illustrated. The plate 6| is assumed to be stationary whereas the plate 62 is assumed to move in accordance with the operation of the service motor 45.

Althoughtheinvention has been illustrated by showing compensation for non-linear variations of transmission line attenuation with temperature changes in the flat gain regulator shown in the patent to F. A. Brooks, No. 2,075,975 it is to be understood that a similar correction may be made in the twist regulator disclosed in the Brooks application.

Modifications in the circuits and in the arrangements and location of parts may be made within the spirit and scope of the invention, and such modifications are intended to be covered by the appended claims.

What is claimed is:

l. A signal transmission line having pilot means associated therewith and subjected to the same temperature changes as the line, a bridge circuit having one arm thereof formed by said pilot means to be controlled according to the temperature changes of said means, galvanometer control mechanism governed by said bridge circuit to have linear operation according to temperature changes of said means, and means controlled by said galvanometer mechanism for governing the transmission line attenuation, for rebalancing the bridge upon each operation and for compensating for the non-linear variations of the line attenuation with temperature changes.

2. A signal transmission line having a pilot path associated therewith and subjected to the same temperature changes as the transmission line, a bridge circuit having one arm thereof formed by said pilot path, mechanism controlled by said bridge according to the resistance variations of the pilot path with temperature changes and means controlled by said mechanism for governing the line attenuation while compensating for non-linear variations of the line attenuation with temperature changes whereby the line attenuation is held constant irrespective of temperature changes.

3. A signal transmission line having non-linear variations in attenuation with temperature changes, pilot means associated therewith and having linear resistance changes with temperature changes, .a bridge circuit having one arm formed by said pilot means, mechanism governed by said bridge and having a linear operation according to temperature changes affecting the transmission line and the pilot. line, and electrical means operated by said mechanism for compensating the non-linear variations of theline attenuation with temperature changes and for controlling the line attenuation to maintain the transmission line attenuation constant irrespective of temperature changes.

4. A signal transmission line having non-linear variations in attenuation with temperature changes, a pilot line associated with said transmission line and subjected to the same temperature changes as said transmission line, a bridge circuit having one arm thereof formed by said Dilot line and varied according to the resistance.

changes of the pilot line with temperature changes, a variable compensating resistance forming another arm of said bridge circuit, galvanometer mechanism controlled by said bridge to have linear operation according to temperature changes of the pilot line, and means operated by said galvanometer mechanism for varying' said compensating resistance to compensate for non-linear variations in the cable attenuation with temperature changes, for rebalancing said bridge and for maintaining the line attenuation constant.

5. A signal transmission line having non-linear variations in attenuation with temperature changes, a pilot line associated with said transmission line and subjected to the same temperature variations as said transmission line, a bridge circuit having one arm thereof formed by said pilot line and varied according to the resistance changes of the pilot line with temperature changes, galvanometer mechanism controlled by said bridge to have linear operation according to temperature changes of the pilot line, and means operated by said galvanometer mechanism for controlling said bridge to compensate for the non-linear variations in the transmission line attenuation with temperature changes, for rebalancing the bridge and for maintaining the attenuation of the transmission line constant.

6. A signal transmission line having non-linear variations in attenuation with temperature changes, pilot means associated with said transmission line and subjected to the same temperature variations as said transmission line, a bridge circuit having one arm thereof formed by said pilot means and controlled according to the resistance changes of the pilot means with temperature changes, mechanism controlled by said bridge to have linear operation according to temperature changes of the pilot means, and means controlled by said mechanism for governing said bridge so as to compensate for non-linear variations in the transmission line attenuation with temperature changes and for maintaining the transmission line attenuation constant.

'7. A signal transmission line having non-linear variations in attenuation with temperature changes, a pilot line associated with said transmission line and subjected to the same temperature changes as said transmission line, a bridge circuit having one arm formed by said pilot line and varied according to the resistance variations of the pilot line with temperature changes, a compensating resistance divided into sections and included in One arm of said bridge, relays for respectively short-circuiting said resistance sections, mechanism controlled by said bridge to have linear operation according to temperature changes of the pilot line, and means controlled by said mechanism for selectively operating said relays to compensate for non-linear variations in the transmission line attenuation with temperature changes and for maintaining the transmission line attenuation constant.

8. A signal transmission line having non-linear variations in attenuation with temperature changes, a pilot line associated with said transmission line and subjected to the same temperature changes as said transmission line, a bridge circuit having one arm formed by said pilot line and varied according to the resistance changes of said pilot line, a compensating resistance divid ed into sections and included in one arm of said bridge, relays respectively associated with said resistance sections for completing short-circuit connections around the resistance sections, means comprising cam members for selectively operating said relays, galvanometer mechanism controlled by said bridge to have linear operation according to temperature changes of the pilot line, and means controlled by said mechanism for operating said cams to control said resistance sections and compensate for non-linear varialtlOllS in the transmission line attenuation with temperature changes, for rebalancing the bridge circuit, and for maintaining the transmission line attenuation constant.

9. A signal transmission line having non-linear variations in attenuation with temperature changes, a pilot line associated with said transmission line and subjected to the same temperature variations as said transmission line, a bridge circuit having one arm formed by said pilot line and varied according to the resistance changes of the pilot line with temperature changes, galvanometer mechanism controlled by said bridge to have linear operation according to temperature changes of the pilot line, and means controlled by said galvanometer mechanism for varying the resistance of said pilot line to compensate for non-linear variations in the transmission line attenuation with temperature changes, for rebalancing the bridge circuit and for maintaining the transmission line attenuation constant.

10. A signal transmission line having a pilot path associated therewith, the transmission line and the pilot path being subjected to the same temperature variations, said path having linear resistance variations according to temperature changes and said transmission line having nonlinear attenuation variations with temperature changes, control means governed by the resistance variations of said pilot path with temperature changes of the pilot path for governing the transmission line attenuation, and means governed by said control means to compensate the non-linear variations of the transmission line attenuation with temperature changes to main tain the line attenuation constant.

JOHN P. KINZER. IRA G. WILSON. 

